Focal structure-function correlation using capillary density and retinal nerve fiber layer thickness in primary open-angle glaucoma

Abstract

Purpose : Correlation between structural (retinal nerve fiber layer thickness (RNFLT)) and functional parameters (visual field deviation (VFD)) can be weak in primary open-angle glaucoma (POAG), especially in advanced disease. Peripapillary capillary density (CD) as assessed by optical coherence tomography angiography (OCTA) may add further information compared to routinely performed RNFLT measurements alone.
The aim of this cross-sectional study was to focally assess the correlation of VFD with both mentioned structural parameters (CD, RNFLT) alone or with their combination for every single visual field test spot (VFS) in POAG.

Methods : In 46 POAG patients, structural OCT for RNFLT measurements, OCTA for peripapillary CD measurements (both Spectralis Heidelberg OCT(A)) and 30-2 standard automated perimetry (Humphrey visual field analyzer) were performed. VFSs were allocated to corresponding RNFLT segments and OCTA slab regions according to a mathematical description of nerve fiber trajectories correcting for disc-fovea distance and disc-fovea angle.
For a total of three regression models - two with focal CD or RNFLT as independent variables (M_CD, M_RNFLT) and one multivariate model including both variables (M_COMBINED) - the Pearson correlation coefficient (r_P) between modelled and measured VFD and the Akaike Information Criterion (AIC) at every VFS were compared.
To identify breakpoints in the relation of focal VFD and CD or RNFLT the Davies test was performed before segmented regression (SR) analysis based on a linear mixed model, which corrected for non-independence of VFSs originating from the same patient, was undertaken.

Results : M_COMBINED showed a mean±SD r_P of 0.710±0.086 with measured focal VFD, while r_Ps for M_CD and M_RNFLT were 0.627±0.078 and 0.578±0.095, respectively. Compared to M_CD an AIC reduction could be observed for 61 VFS in M_COMBINED, while this was the case for 71 VFS in M_COMBINED when compared to M_RNFLT .
Upon SR analysis, a significant breakpoint was detected at −9.43 dB VFD (CI −8.38, −10.57 dB) for CD and at −8.46 dB VFD (CI −9.68, −7.25 dB) for RNFLT.

Conclusions : In this study VFSs were allocated to peripapillary locations with yet unsurpassed granularity. Our results emphasize the capacity of OCTA in glaucoma diagnostic algorithms and suggest that combining peripapillary RNFLT and OCTA-derived CD may be diagnostically advantageous in POAG patients.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.